LaMotte Air Pollution Sampling & Measurement - Manual (Page 3)

HOW TO ESTABLISH A MEANINGFUL
AIR MONITORING PROGRAM
To set up a program for monitoring air pollution there are two basic
requirements. First, a means of collecting and analyzing the air sample is
required. Second, a strategic plan for continuous sampling at a series of
logical monitoring sites must be established. The recording of data over
a period of time is important in observing the variations that take place
at the monitoring sites.
EQUIPMENT REQUIREMENTS
Most of the sampling in air pollution studies is done with some type of
vacuum equipment. The vacuum is required to draw an air sample
through a chamber holding a special absorbing solution. The absorbing
solution is chemically selective for a particular gas, and is held in a
special glass bubbling tube called an impinger. Since gaseous pollutants
differ chemically, the absorbing solutions are also different.
In order to make a quantitative test, a means to measure the amount of
air that is drawn through the absorbing solution has to be known. This is
done by the use of an adjustable flowmeter. A flowmeter is simply a
device to measure the rate of flow of the air through the absorbing
solution. For most air pollution studies the flowmeter is calibrated to
measure the rate of flow in liters per minute (Lpm).
When a flowmeter is attached to the vacuum portion of the air sampling
train, one can accurately monitor the amount of air which is pulled
through the absorbing solution. A flowmeter with an adjustable flow
device - like a needle valve - can be used to preset the vacuum pump to
sample at a known rate. If one draws air through the absorbing solution
at 2.0 Lpm for 10 minutes, then 20 liters of air have been sampled.
As one of the most important components of the air sampling train, the
vacuum pump must meet certain requirements. If one is interested in
taking air samples from outdoors, the vacuum equipment must be
battery operated and completely portable. It should also possess a
means for regulating the amount of air sampled. Vacuum equipment
meeting these criteria would be useful for most applications. Air pumps
that push the air through the pump first and then through the impinging
equipment should be avoided. Proper sampling techniques require that
the air sample be “sucked” through the impinger prior to its contact with
the pump. The pump should have the ability to maintain a particular
flow rate for a pre-determined time. Air sampling equipment should be
completely portable, possess a regulating device for sampling at
different rates, and be able to maintain a particular sampling rate for a
known amount of time.
Air Pollution Sampling & Measurement 3